MKKRLUI : TRIASSIC KM1TI! YOSATKIA. !)5 



Caudal vertebrae with Y-shaped chevrons. Rib articulation mainly single- 

 headed, with a disposition to divide indistinctly shown in the posterior dorsal 

 and anterior caudal regions. Inferior pelvic elements plate-like. Interclavicle 

 tending to assume a triangular rather than a T-shaped form. Anterior limbs 

 and arches considerably larger than posterior. Humerns not relatively elon- 

 gated compared with Ichthyoxinn-iis, in some instances much abbreviated or 

 broadened. Epipodial elements relatively elongated, radius with median con- 

 striction, ulna convex on posterior border. Digits five, maximum number of 

 phalanges ten to eleven in the longest digit. Phalanges generally somewhat 

 elongated and with median constriction or lateral notch. Elements of poste- 

 rior limbs generally less specialized than those of anterior limb. Skull rela- 

 tively large compared with size of trunk. Facial region relatively short and 

 maxillary relatively long compared with the form in Ichthyosaurus. Orbits 

 large. Dentition showing some differentiation, anterior teeth slender-conical, 

 posterior teeth blunt-conical. Teeth rather widely spaced, and set mainly in 

 distinct pits. 



The genus Mixosaurux was based by Baur on Bassani's Ichthyosaurus 

 conniJitnuis of the bituminous shales in the Upper Triassic of Besano in 

 northern Italy. Though material from other regions and other horizons has 

 been referred to this genus, it is not certain that any of these forms really 

 represent Mifowuirns. In the following discussion only the typical material 

 from Italy is referred to this genus. The other forms may be doubtfully re- 

 ferred to this group or may be referred to other genera, as will be indicated 

 elsewhere. 



Known only from the Triassic. 



.MIXOSAURUS CORNALIANUS (Bassani). 



Iclitliuoxnurus cornaliunus Bassani, Atti della Soc. Ital. di Sc. Nat., vol. 29, p. 15. 

 Mijrosaurux conHiliaimx (Baur), Ber. d. 20 Versam. d. Oberrh. Geol. Ver., 1887, p. 19. 

 Mixoftintnix i-ornaUanus (Repossi), Atti della Soc. Ital. di Sc. Nat., vol. 41, p. 7. 



The material representing this species now in the Civic Museum of Milan 

 includes a number of very excellent specimens, well illustrating the structure 

 of nearly all of the important parts of the skeleton. The descriptions of 

 Bassani and Baur having given only a suggestion of the characters present in 

 this interesting animal, Dr. E. Repossi (1902) has made a satisfactory com- 

 parison with this material possible, through the publication of a number of 

 excellent figures accompanied by a general description of the skeleton. 



The specimens known are mostly small forms only a few feet in length. 

 There are a few remains of larger individuals, but the average size of the forms 

 is small compared with most other known ichthyosaurian groups. In contrast 



